Help Finding Affordable Roll-Neck

I bought my first rollneck jumper this season and I'm addicted, I love the aesthetic it creates, classic but relaxed. It also does wonders for covering up my lanky neck. Unfortunately, they don't pop up on the highstreet much. I would like one in a student budget, so that probably means less that £50.

Other specifics: it needs to be fine-knit, slim fitting. I'm looking for black or navy.